1. Field of the Invention
This invention relates to well drilling operations and, more particularly, to a device for assisting in the assembly of pipe strings, such as casing strings, drill strings and the like.
2. Description of the Related Art
The drilling of oil wells involves assembling drill strings and casing strings, each of which comprises a plurality of elongated, heavy pipe segments extending downwardly from an oil drilling rig into a hole. The drill string consists of a number of sections of pipe which are threadedly engaged together, with the lowest segment (i.e., the one extending the furthest into the hole) carrying a drill bit at its lower end. Typically, the casing string is provided around the drill string to line the well bore after drilling the hole and ensure the integrity of the hole. The casing string also consists of a plurality of pipe segments which are threadedly coupled together and formed with through passages sized to receive the drill string and/or other pipe strings.
The conventional manner in which plural casing segments are coupled together to form a casing string is a labor-intensive method involving the use of a xe2x80x9cstabberxe2x80x9d and casing tongs. The stabber is manually controlled to insert a segment of casing into the upper end of the existing casing string, and the tongs are designed to engage and rotate the segment to threadedly connect it to the casing string. While such a method is effective, it is cumbersome and relatively inefficient because the procedure is done manually. In addition, the casing tongs require a casing crew to properly engage the segment of casing and to couple the segment to the casing string. Thus, such a method is relatively labor-intensive and therefore costly. Furthermore, using casing tongs requires the setting up of scaffolding or other like structures, and is therefore inefficient.
Others have proposed a casing running tool for assembling casing strings which utilizes a conventional top drive assembly. The tool includes a pivotable manipulator which is designed to engage a pipe segment and raise the pipe segment up into a power assist spider, which relies on gravity to hold the pipe segment. The spider is coupled to the top drive and may be rotated by it. Thus, the pipe segment may be brought into contact with a casing string and the top drive activated to rotate the casing segment and threadedly engage it with the casing string.
While such a system provides benefits over the more conventional systems used to assemble casing strings, such a system suffers from shortcomings. One such shortcoming is that the casing segment may not be sufficiently engaged by the power assist spider to properly connect the casing segment with the casing string. In addition, the system fails to provide any means for effectively controlling the load applied to the threads at the bottom of the casing segment, as well as to the top of the casing string when the casing segment is lowered onto the string. Without the ability to control these loads, cross-threading may occur, resulting in stripped threads and a useless casing segment.
Accordingly, it will be apparent to those skilled in the art that there continues to be a need for a device for use in a drilling system which utilizes an existing top drive assembly to efficiently assemble casing and/or drill strings, and which positively engages a pipe segment to ensure proper coupling of the pipe segment to a pipe string. In addition, the need exists for a load compensator to compensate for both upwardly and downwardly directed loads that are applied to either the casing string or the casing segment. The present invention addresses these needs and others.
Briefly, and in general terms, the present invention is directed to a pipe running tool for use in drilling systems and the like to assemble casing and/or drill strings. The pipe running tool is coupled to an existing top drive assembly which is used to rotate a drill string, and includes a powered elevator that is powered into an engaged position to securely engage a pipe segment, for example, a casing segment. Because the elevator is powered into the engaged position, the pipe segment may be properly coupled to an existing pipe string using the top drive assembly.
The system of the present invention in one illustrative embodiment is directed to a pipe running tool mountable on a rig and including: a top drive assembly adapted to be connected to the rig for vertical displacement of the top drive assembly relative to the rig, the top drive assembly including a drive shaft, the top drive assembly being operative to rotate the drive shaft; and a lower pipe engagement assembly including a central passageway sized for receipt of the pipe segment, the lowerpipe engagement assembly including a powered engagement device that is powered to an engaged position to securely and releasably grasp the pipe segment, the lower pipe engagement assembly being in communication with the drive shaft, whereby actuation of the top drive assembly causes the lower pipe engagement assembly to rotate.
In another illustrative embodiment, the present invention is directed to a method of assembling a pipe string, including the steps of: actuating a lower pipe engagement assembly to releasably engage a pipe segment; lowering a top drive assembly to bring the pipe segment into contact with a pipe string; monitoring the load on the pipe string; actuating a load compensator to raise the pipe segment a selected distance relative to the pipe string, if the load on the pipe string exceeds a predetermined threshold value; and actuating the top drive assembly to rotate the pipe segment to threadedly engage the pipe segment and pipe string.
In yet another embodiment, the invention is directed to a load compensator for use in connection with a pipe running tool. The load compensator includes an outer housing connected to the pipe running tool that holds the pipe segment. A piston is disposed within the housing, and is connected to a top drive system. The housing includes a first port through which pressurized air is delivered inside the housing to drive the piston within the housing. A second port is disposed at a selected location on the housing, such that when the piston is advanced past the second port, pressurized air passes through the port, and causes the control circuit to stop delivering air through the first port. Once pressurized air no longer flows through the second port, the control circuit causes air to be delivered to the first port.
Other features and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the features of the present invention.